1. Field of the Invention
The present invention relates to aluminosilicate compositions and the catalytic conversion of synthesis gas to low molecular weight hydrocarbons utilizing these compositions.
2. Discussion of the Prior Art
Zeolite materials, both natural and synthetic, are known to have catalytic capability for various types of reactions, especially hydrocarbon conversions. The well known crystalline aluminosilicate zeolites are commonly referred to as "molecular sieves" and are characterized by their highly ordered crystalline structure and uniformly dimensioned pores, and are distinguishable from each other on the basis of composition, crystal structure, adsorption properties and the like. The term "molecular sieves" is derived from the ability of the zeolite materials to selectively adsorb molecules on the basis of their size and form.
The processes for producing such crystalline synthetic zeolites are well known in the art. A family of crystalline aluminosilicate zeolites, designated ZSM-5, is disclosed in U.S. Pat. No. 3,702,886, said patent being incorporated herein by reference.
U.S. Pat. No. 3,941,871 relates to novel crystalline metal organosilicates which are essentially free of Group IIIA metals, i.e., aluminum and/or gallium. This patent is incorporated herein by reference. It is noted therein that the amount of alumina present in the known zeolites appears directly related to the acidity characteristics of the resultant product and that a low alumina content has been recognized as being advantageous in attaining a low degree of acidity which in many catalytic reactions is translated into low coke making properties and low aging rates. A typical procedure for making the organosilicates is to react a mixture containing a tetraaklylammonium compound, sodium hydroxide, and oxide of a metal other than a metal of Group IIIA, an oxide of silicon, and water until crystals of said metal organosilicates are formed. It is also noted in the patent that the family of crystalline metal organosilicates have a definite X-ray diffraction pattern which is similar to that of the ZSM-5 zeolites. Minor amounts of alumina are contemplated in the patent and are attributable primarily to the presence of aluminum impurities in the reactants and/or equipment employed.
U.S. Pat. No. 3,884,835 discloses crystalline silica compositions. The crystalline silica materials may also contain a metal promoter which may be selected from Group IIIA, Group VB or Group VIB elements. Boron is disclosed as one of the metal promoters.
U.S. Pat. No. 4,088,605 is directed to the synthesis of a zeolite, such as ZSM-5, which contains an outer shell free from aluminum. The patent states at column 10, the paragraph beginning at line 20, that to produce the outer aluminum-free shell, it is also essential that the reactive aluminum be removed from the reaction mixture. It is therefore necessary, as noted therein, to process the zeolite and to replace the crystallization medium with an aluminum-free mixture to obtain crystallization of SiO.sub.2 on the surface of the zeolite which can be accomplished by a total replacement of the reaction mixture or by complexing from the original reaction mixture any remaining aluminum ions with reagents such as gluconic acid or ethylenediaminotetraacetic acid (EDTA).
Crystalline borosilicate compositions are disclosed in Germany Offenlegungschrift 2,746,790. This application relates specifically to borosilicates which are prepared using the usual procedures for making the aluminosilicate zeolites. It is noted therein that in instances where a deliberate effort is made to eliminate aluminum from the borosilicate crystal structure because of its adverse influence on particular conversion processes, the molar ratios of SiO.sub.2 /Al.sub.2 O.sub.3 can easily exceed 2000-3000 and that this ratio is generally only limited by the availability of aluminum-free raw materials.
Germany Offenlegungschrift 2,848,849 relates to crystalline aluminosilicates of the ZSM-5 zeolite series. These particular zeolites have a silica to alumina mole ratio greater than 20 and are prepared from a reaction mixture containing a source of silica, alumina, a quaternary alkyl ammonium compound and a metal compound including such Group VIII metals as ruthenium, palladium and platinum. In Example 2, the crystalline aluminosilicate is prepared from a reaction mixture containing RuCl.sub.3 and in Example 3, the reaction mixture contains H.sub.2 PtCl.sub.6.nH.sub.2 O.
U.S. Patent No. 4,468,474 discloses hydrogen activated catalyst compositions comprising iron, silicon and carbon that selectively convert gaseous mixtures to C.sub.2 -C.sub.6 alkenes. It is further noted that the catalysts maintained their activity and high selectivity over a long period and that regeneration of partially deactivated catalysts can be accomplished by treatment with hydrogen at elevated temperature.
U.S. Pat. No. 4,298,695 discloses the conversion of sythesis gas to a liquid hydrocarbon, e.g. naphtha. The process employs unpromoted catalysts which need promoters and high activity without aging is characteristic of these catalysts.
U.S. Pat. No. 4,481,155 discloses a process for the conversion of synthesis gas utilizing a catalyst which comprises a ZSM-5 type zeolite and a carbon oxide reducing component. This process yields a particular product, e.g. linear alpha-olefins, (C.sub.4 -C.sub.6 olefins).
U.S. Pat. No. 4,732,535 discloses a process for the conversion of synthesis gas to an exclusive hydrocarbon product with selectivity to ethane. The catalysts comprise a crystalline zeolite component and a metal component. The zeolites employed are primarily synthetic zeolites such as ZSM-5, ZSM-11 and the like, that have a silica:alumina ratio of at least 12:1 and preferably 30:1. The metal component may be derived from one or more metals. Suitable metals or combinations of metals are those which may be employed for the synthesis of alcohols from synthesis gas. The metal components may be introduced into the zeolite by impregnation from liquid ammonia solutions. In Example 10, the effect of using different zeolites, e.g. erionite (a natural zeolite) is shown in the conversion of synthesis gas. Erionite shows significantly lower selectivity for ethane.
While the art has provided zeolitic catalysts having a wide variety of catalytic and adsorbtive properties, the need still exists for crystalline materials having different and/or enhanced catalytic properties. For example, an important use for a catalytic material is the conversion of synthesis gas to low molecular weight hydrocarbons. Further, many hydrocarbon conversion processes are performed employing zeolites, i.e. alkylation and isomerization. As is well-known in the art, it is important to maximize selectivity for a desired product. Accordingly it is one object of the present invention to provide novel crystalline aluminosilicate compositions.
Accordingly it is another object of this invention to provide aluminosilicate compositions having different and enhanced catalytic properties.
Another object of the invention herein is to provide a new method for the preparation of these novel crystalline aluminosilicate compositions.
A further object of this invention is to provide an improved method for the conversion of hydrocarbons and oxygenated compounds to selected end products.
A still further object of this invention is to provide an improved method for the conversion of synthesis gas to low molecular weight hydrocarbons utilizing aluminosilicate compositions.
The achievement of these and other objects will be apparent from the following description of the subject invention.